Controlling a dispatch operation of an energy storage system

ABSTRACT

Systems and methods of controlling a dispatch operation of an energy storage system are provided. In particular, a degradation value of a present dispatch state of an energy storage system can be determined. The present dispatch state can specify one or more energy storage units presently coupled to the system. The degradation value can be determined based at least in part on one or more operating parameters, such as temperature, open circuit voltage, charge or discharge current, and/or contactor life. The degradation value can then be compared against one or more degradation values associated with one or more candidate dispatch states. A dispatch state can then be selected based on the comparison. One or more energy storage units can be selectively coupled to the energy storage system based at least in part on the selected dispatch state.

FIELD OF THE INVENTION

The present subject matter relates generally to energy storage systemsand more particularly, to systems and methods of controlling a dispatchoperation of one or more energy storage units in an energy storagesystem.

BACKGROUND OF THE INVENTION

Energy storage systems have become increasingly used to deliver power toutility grids either as part of standalone energy storage systems or aspart of a renewable energy farm (e.g., a wind farm or solar farm) withan integrated energy storage system. Energy storage systems can includeone or more battery banks or other energy storage units that can becoupled to the grid or other load via a suitable power converter. Energystorage systems are unique in that energy storage systems have theability to both deliver and reserve energy for particular grid services.

Different energy storage units can perform differently in variousoperating conditions associated with an energy storage system. Forinstance, energy storage units can accumulate degradation and/orinefficiency in various operating conditions. As an example, sodiummetal halide batteries can experience capacity fade at low dischargerates. As another example, sodium metal halide batteries can experienceresistance rise effects at high voltage recharge rates. Such degradationand inefficiency can lead to a reduced lifespan of an energy storagesystem. Thus, there is a need for systems and methods of controlling anenergy storage system to reduce inefficiency and/or degradation.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of embodiments of the present disclosure will beset forth in part in the following description, or may be learned fromthe description, or may be learned through practice of the embodiments.

One example aspect of the present disclosure is directed to a method ofcontrolling a dispatch operation of an energy storage system. The methodincludes receiving, by one or more control devices, data indicative of apresent dispatch state associated with an energy storage system. Theenergy storage system includes a plurality of energy storage unitscoupled in parallel. The present dispatch state specifies the energystorage units presently coupled to the system. The method furtherincludes identifying, by the one or more control devices, one or morecandidate dispatch states associated with the energy storage system.Each of the one or more candidate dispatch states is different from thepresent dispatch state. The method further includes selecting, by theone or more computing devices, at least one of the one or more candidatedispatch states as a selected dispatch state based at least in part on aperformance model. The performance model models the performance of theone or more candidate dispatch states as a function of one or moreoperating parameters. The method further includes controlling, by theone or more control devices, operation of the energy storage systembased at least in part on the selected dispatch state.

Another example aspect of the present disclosure is directed to anenergy storage system. The energy storage system includes a plurality ofenergy storage units coupled in parallel. The energy storage systemfurther includes a system controller communicatively coupled to theplurality of energy storage units. The system controller includes atleast one processor and a non-transitory computer-readable mediumstoring instructions that, when executed by the at least one processor,cause the system controller to perform operations. The operationsinclude receiving data indicative of a present dispatch state associatedwith an energy storage system. The energy storage system includes aplurality of energy storage units coupled in parallel. The presentdispatch state specifies the energy storage units presently coupled tothe system. The operations further include identifying one or morecandidate dispatch states associated with the energy storage system.Each of the one or more candidate dispatch states is different from thepresent dispatch state. The operations further include selecting atleast one of the one or more candidate dispatch states as a selecteddispatch state based at least in part on a performance model. Theperformance model models the performance of the one or more candidatedispatch states as a function of one or more operating parameters. Theoperations further include controlling operation of the energy storagesystem based at least in part on the selected dispatch state.

Yet another example aspect of the present application is directed to asystem controller for controlling one or more energy storage units in anenergy storage system. The system controller includes at least oneprocessor and a non-transitory computer-readable medium storinginstructions that, when executed by the at least one processor, causethe system controller to perform operations. The operations includereceiving data indicative of a present dispatch state associated with anenergy storage system. The energy storage system includes a plurality ofenergy storage units coupled in parallel. The present dispatch statespecifies the energy storage units presently coupled to the system. Theoperations further include identifying one or more candidate dispatchstates associated with the energy storage system. Each of the one ormore candidate dispatch states is different from the present dispatchstate. The operations further include selecting at least one of the oneor more candidate dispatch states as a selected dispatch state based atleast in part on a performance model. The performance model models theperformance of the one or more candidate dispatch states as a functionof one or more operating parameters. The operations further includecontrolling operation of the energy storage system based at least inpart on the selected dispatch state.

Variations and modifications can be made to these example aspects of thepresent disclosure.

These and other features, aspects and advantages of various embodimentswill become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the present disclosure and, together with thedescription, serve to explain the related principles.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed discussion of embodiments directed to one of ordinary skill inthe art are set forth in the specification, which makes reference to theappended figures, in which:

FIG. 1 depicts an example energy storage system according to exampleembodiments of the present disclosure;

FIG. 2 depicts aspects of an example controller according to exampleembodiments of the present disclosure;

FIG. 3 depicts an example control topology for an example control systemaccording to example embodiments of the present disclosure;

FIG. 4 depicts a flow diagram of an example method of controlling adispatch operation of an energy storage system according to exampleembodiments of the present disclosure; and

FIG. 5 depicts a flow diagram of an example method of controlling adispatch state of an energy storage system over one or more incrementaltime periods according to example embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

Example aspects of the present disclosure are directed to controlling adispatch operation of a plurality of energy storage units in an energystorage system. In particular, a number of energy storage units can bedispatched (e.g., coupled to the energy storage system) to meet a powerdemand provided, for instance, by a power grid or other source. Anenergy storage unit may include one or more electrochemical cells. Theplurality of energy storage units can make up a portion of an energystorage system. The energy storage system can include a plurality ofenergy storage units located on a single electrical bus, and/or aplurality of energy storage units remotely distributed using multipleelectrical busses. Each energy storage unit can be coupled to a switch(e.g. one or more contactors). The switch can be selectively operable tocouple the energy storage unit to a load (e.g. power grid or otherload). In particular, the switch can include an open state and a closedstate. The energy storage unit can be coupled to the system when theswitch is in the closed state, and decoupled from the system when theswitch is in the open state.

In example embodiments, upon receiving a power demand or commitment fora power grid or other load, a present dispatch state and a plurality ofcandidate dispatch states associated with the energy storage system canbe identified. The present dispatch state can specify the energy storageunits that are presently coupled to the system and the energy storageunits that are presently decoupled from the system. Each candidatedispatch state can specify the energy storage units to potentially becoupled to the system and the energy storage units that are topotentially be decoupled from the system. In example embodiments, eachcandidate dispatch state can be different from the present dispatchstate.

A degradation value can then be calculated for the present dispatchstate and each candidate dispatch state. In particular, the degradationvalue for a dispatch state can be calculated at least in part byaccessing a performance model associated with the energy storage system.The performance model can receive one or more inputs to determine adegradation value or other data indicative of one or more efficiencyand/or degradation characteristics associated with the present dispatchstate and each of the candidate dispatch states. The one or more inputscan include one or more operating parameters associated with thedispatch states. For instance, the one or more operating parameters caninclude data related to temperature, open circuit voltage, currentand/or contactor life associated with each of the energy storage unitsto be coupled to the system. In this manner, the degradation value canbe indicative of efficiency and/or degradation characteristics of theenergy storage system, which can correspond to an overall life cycleperformance trajectory associated with the energy storage system.

In example embodiments, the performance model can further take intoaccount one or more operating constraints, such as for instance, powerdemand, battery power, battery current, voltage characteristic, and/orbattery temperature. The one or more operating constraints may changeover time. For instance, the power demand may change at various times ofthe day (and/or various times of the year) based at least in part onfluctuating grid conditions.

In addition, the performance model can take into account performancedegradation for individual storage units to determine selection of unitsto couple and decouple from the system to improve performance. Forinstance, the model can take into consideration which energy storageunits were previously coupled in a dispatch state so that a new dispatchstate does not provide for the coupling or decoupling the same energystorage unit to the system each time a new dispatch state is determined.

Operation of the energy storage system can be controlled based at leastin part on the degradation values of the candidate dispatch states ofthe energy storage system relative to the present dispatch state. Forinstance, a candidate dispatch state can be selected as a selecteddispatch state based on the degradation value. The energy storage systemcan then be controlled by coupling the number of energy storage units tothe system as specified by the selected dispatch state.

In this way, example aspects of the present disclosure can have atechnical effect of improving the efficiency of an energy storage systemby adjusting a dispatch state of the energy storage system based atleast in part on one or more operating parameters. Similarly, exampleaspects of the present disclosure can have a technical effect ofreducing degradation associated with an energy storage system byadjusting a dispatch state of the energy storage system based at leastin part on one or more operating parameters.

In example embodiments, the energy storage system can be furthercontrolled based at least in part on the one or more operatingconstraints. For instance, in such embodiments, a candidate dispatchstate may only be selected if controlling the energy storage system inaccordance with the candidate dispatch state would cause the energystorage system to operate within the bounds of the constraints. Forinstance, a candidate dispatch may only be selected if the energystorage system would output enough power to meet the power demand whileoperating in accordance with the candidate dispatch state. In thismanner, a candidate dispatch state can be selected to meet a near termpower commitment (e.g. power delivery or power acceptance) associatedwith a power application. As another example, a candidate dispatch statemay only be selected if operating the energy storage system inaccordance with the candidate dispatch state would cause the energystorage system to operate at a temperature below a predeterminedtemperature. As yet another example, the energy storage system can becontrolled based at least in part on a state of charge differencebetween energy storage units. In this manner, a candidate dispatch maybe selected only if operating the energy storage system in accordancewith the candidate dispatch state would cause the state of chargedifference between the energy storage units in the energy storage systemto be maintained below a threshold.

In example embodiments, the plurality of candidate dispatch states caninclude every possible dispatch state (e.g. every possible combinationof energy storage units that can be coupled to the system). Forinstance, each candidate dispatch state combination can be identifiedduring one or more time periods. A degradation value can be calculatedfor each possible dispatch state. Operation of the energy storage systemcan then be controlled in accordance with the candidate dispatch statehaving the optimal degradation value. For instance, the optimaldegradation value can be the lowest degradation value of the pluralityof degradation values.

In alternative embodiments, one or more candidate dispatch states can beidentified by incrementally adjusting a number of energy storage unitsto be coupled to the system during a plurality of incremental timeperiods. Degradation values for each candidate dispatch state can becalculated during each incremental time period. For instance, anoptimization routine can be used to identify one or more candidatedispatch states by periodically adjusting the number of energy storageunits to be coupled to the system in an incremental manner. Inparticular, incrementally adjusting the number of energy storage unitsto be coupled to the system can include increasing or decreasing thenumber of energy storage units to be coupled to the system relative tothe number of energy storage units specified by the candidate dispatchstate in accordance with which the energy storage system is presentlyoperating.

Each incremental adjustment can have an effect on the degradation valueof the energy storage system. For instance, each incremental adjustment(e.g. incremental increase or incremental decrease) can cause thedegradation value of the energy storage system to increase, decrease, orremain constant. In example embodiments, the optimization routine canfurther include, for each time period, comparing the degradation valueassociated with the present candidate dispatch state (e.g. the mostrecently determined degradation value) to the degradation valueassociated with the candidate dispatch state identified in a previoustime period (e.g. a previous candidate dispatch state). For instance,the degradation value associated with the present candidate dispatchstate can be compared to the degradation value of the present dispatchstate.

In example embodiments, if the degradation value associated with thepresent candidate dispatch state is less than the degradation valueassociated with the previous candidate dispatch state, the optimizationroutine can include selecting the present candidate dispatch state as aselected dispatch state. Operation of the energy storage system can thenbe controlled in accordance with the selected dispatch state.Controlling the operation of the energy storage system in this mannercan include, for instance, controlling the operating state of one ormore switches coupled to one or more energy storage units such that thenumber of energy storage units coupled to the system corresponds to thenumber specified in the selected candidate dispatch state.

If the degradation value associated with the present candidate dispatchstate is not less than the degradation value associated with theprevious incremental adjustment, the present candidate dispatch statemay not be selected and operation of the energy storage system can becontrolled such that no change is made to the dispatch state of theenergy storage system. In particular, operation of the energy storagesystem can be controlled to maintain operation in accordance with thedispatch state selected most recently (e.g. the dispatch state inaccordance with which the energy storage system is presently operating).

In example embodiments, if the degradation value associated with thepresent candidate dispatch state is greater than the degradation valueassociated with the previous candidate dispatch state, the optimizationroutine can include changing the direction of adjustment. For instance,if the present candidate dispatch state corresponds to an incrementalincrease in the number energy storage units to be coupled to the systemrelative to the previous candidate dispatch state, and to an increase indegradation value relative to the previous candidate dispatch state, thenext identified candidate dispatch state can correspond to a decrease inthe number of energy storage units to be coupled to the system. In thismanner, the direction of adjustment can change based at least in part onthe degradation value to identify a desired degradation value.

With reference now to the Figures, example embodiments of the presentdisclosure will now be discussed in detail. FIG. 1 depicts an examplepower system 100 that includes an energy storage system 110 according toexample aspects of the present disclosure. The power system 100 can be astandalone power generation system or can be implemented as part of arenewable energy system, such as wind farm or solar farm.

The power system 100 can include a battery energy storage system (BESS)110. The BESS 110 can include one or more battery energy storage units112, such as battery cells or battery packs. The battery energy storageunits 112 can contain one or more sodium nickel chloride batteries,sodium sulfur batteries, lithium ion batteries, nickel metal hydridebatteries, or other similar devices. The battery energy storage units112 can be coupled to a switching element (e.g. one or more contactors)selectively operable to couple the energy storage units 112 to thesystem 100. Although battery energy storage units 112 include individualbattery cells coupled to a switching element, it will be appreciatedthat battery energy storage units 112 can include multiple battery cellscoupled to the switching element. In addition, the present disclosure isdiscussed with reference to a battery energy storage system for purposesof illustration and discussion, those of ordinary skill in the art,using the disclosures provided herein, should understand that otherenergy storage devices (e.g. capacitors, fuel cells, etc.) can be usedwithout deviating from the scope of the present disclosure.

The BESS 110 can include a battery management system (BMS) 115. The BMS115 can include one or more electronic devices that monitor one or moreof the battery energy storage units 112, such as by protecting thebattery energy storage unit from operating outside a safe operatingmode, monitoring a state of the battery energy storage unit, calculatingand reporting operating data for the battery energy storage unit,controlling the battery energy storage unit environment, and/or anyother suitable control actions. For example, in several embodiments, theBMS 115 is configured to monitor and/or control operation of one or moreenergy storage units 112. The BMS 115 can be, for example, a logiccontroller implemented purely in hardware, a firmware-programmabledigital signal processor, or a programmable processor-basedsoftware-controlled computer.

The BESS 110 can optionally be coupled to a DC to DC converter 120. TheDC to DC converter 120 can be a buck converter, boost converter, orbuck/boost converter. The DC to DC converter 120 can convert a DCvoltage at the DC bus 125 to a suitable DC voltage for providing powerto or receiving power from the BESS 110. The DC bus 125 can be astandalone DC bus between the DC to DC converter 120 and the inverter130. Alternatively, the DC bus 125 can be a DC bus of a two-stage powerconverter used to convert energy from a renewable energy source tosuitable power for the AC grid 150.

The DC to DC converter can include one or more electronic switchingelements, such as insulated gate bipolar transistors (IGBT). Theelectronic switching elements can be controlled (e.g. using pulse widthmodulation) to charge or to discharge the battery energy storage system110. In addition, the electronic switching elements can be controlled tocondition DC power received or provided to the BESS 115.

The power system can further include and inverter 130. The inverter 130can be configured to convert DC power on the DC bus 125 to suitable ACpower for application to utility grid 150 (e.g. 50 Hz or 60 Hz ACpower). The inverter 130 can include one or more electronic switchingelements, such as IGBTs. The electronic switching elements can becontrolled (e.g. using pulse width modulation) to convert the DC poweron the DC bus to suitable AC power for the grid 150. The inverter 130can provide AC power to the grid 150 through a suitable transformer 140and various other devices, such as switches, relays, contactors, etc.used for protection of the power system 100.

The power system 100 can also include a controller 200 that isconfigured to monitor and/or control various aspects of the power system100 as shown in FIGS. 1, 2, and 3. For example, the controller 200 canbe configured to control the energy storage system to selectively coupleenergy storage units to the system 100 based at least in part on aperformance model according to example aspect of the present disclosure.In accordance with various embodiments, the controller 190 can be aseparate unit (as shown) or can be part of the BMS 115 of the BESS 110.

Referring particularly to FIG. 2, controller 200 can have any number ofsuitable control devices. The controller 200 can be a system levelcontroller (e.g., farm level controller) or a controller of one or moreindividual energy storage units. As illustrated, for example, controller200 can include one or more processor(s) 212 and one or more memorydevice(s) 214 configured to perform a variety of computer-implementedfunctions and/or instructions (e.g., performing the methods, steps,calculations and the like and storing relevant data as disclosedherein). The instructions when executed by processor(s) 212 can causeprocessor(s) 212 to perform operations according to example aspects ofthe present disclosure. For instance, the instructions when executed byprocessor(s) 212 can cause processor(s) 212 to implement one or morecontrol routines, such as the optimizer as will be discussed in moredetail below.

Additionally, controller 200 can include a communications system 220 tofacilitate communications between controller 200 and the variouscomponents of the system 100. Further, communications system 220 caninclude a sensor interface 222 (e.g., one or more analog-to-digitalconverters) to permit signals transmitted from one or more sensors 223,224, and 225 to be converted into signals that can be understood andprocessed by processor(s) 212. It should be appreciated that sensors223-225 can be communicatively coupled to communications system 220using any suitable means, such as a wired or wireless connection. Thesignals can be communicated using any suitable communications protocol.

As such, processor(s) 212 can be configured to receive one or moresignals from sensors 223-225. For instance, processor(s) 212 can receivesignals indicative of the state of charge of energy storage units 102from a monitoring device configured to monitor a state of charge ofenergy storage units 102 in energy storage system 100. Processor(s) 212can also receive signals indicative of power delivery (e.g., amount ofpower charging/discharging) from additional sensors.

As used herein, the term “processor” refers not only to integratedcircuits referred to in the art as being included in a computer, butalso refers to a controller, a microcontroller, a microcomputer, aprogrammable logic controller (PLC), an application specific integratedcircuit, and other programmable circuits. The processor is alsoconfigured to compute advanced control algorithms and communicate to avariety of Ethernet or serial-based protocols (Modbus, OPC, CAN, etc.).

Additionally, the memory device(s) may generally comprise memoryelement(s) including, but not limited to, computer readable medium (e.g.random access memory (RAM)), computer readable non-volatile medium (e.g.read-only memory, or a flash memory), a floppy disk, a compact disc-readonly memory (CD-ROM), a magneto-optical disk (MOD), a digital versatiledisc (DVD) and/or other suitable memory elements. Such memory device(s)may generally be configured to store suitable computer-readableinstructions that, when implemented by the processor(s), configureprocessor(s) 212 to perform the various functions as described herein.The memory may be a separate component from the processor or may beincluded onboard within the processor.

Controller 200 can also include or store data associated with aperformance model 218. Generally, the model 218 can model energy storageunits 102 by describing expected behavior of the units under certaindescribed circumstances and in view of various operating parameters(e.g. one or more of open circuit voltage, temperature, current, orcontactor life associated with energy storage units 102). As will bedescribed in more detail below, performance model 218 can be configuredto determine a degradation value for a present set of dispatched energystorage units (e.g. present dispatch state), and degradation values fora plurality of candidate sets of energy storage units to be potentiallybe dispatched (e.g. candidate dispatch states).

Controller 200 can also include an optimizer 216. The optimizer 216 canbe computer logic utilized to provide desired functionality, such as atleast a portion of an optimization routine associated with energystorage system 100. Thus, the optimizer 216 can be implemented inhardware, firmware and/or software controlling a general purposeprocessor. In one embodiment, the optimizer 216 includes program codefiles stored on the storage device, loaded into memory and executed by aprocessor or can be provided from computer program products, forexample, computer executable instructions that are stored in a tangiblecomputer-readable storage medium such as RAM hard disk or optical ormagnetic media. In particular, as will be described in greater detailbelow, the optimizer 216 to determine an optimum or near optimumdispatch state based at least in part on the performance model. As usedherein, near optimum refers to within 25% of an optimum solution.

In some embodiments, optimizer 216 and/or the performance model 218 canfurther take into account one or more constraints. The one or moreconstraints can include a power demand or commitment, power, current,voltage characteristic, or temperature associated with energy storageunits 102. In this manner, optimizer 216 can select one or more dispatchstates as selected dispatch states based at least in part on thecomparison of the degradation values and based at least in part on theconstraints.

FIG. 3 depicts an example control topology 300 for an energy storagesystem according to example embodiments of the present disclosure. Asdepicted, performance model 218 can access, obtain, or receive varioustypes of data, including operating parameters 302, and system constraintdata 304. Operating parameters 302 and constraint data 304 can beprovided from one or more sources. For instance, some data may beobtained by sensors 223-225. Some data may be accessed over a network(e.g., Internet) from various sources. For instance, when energy storageunits 102 are remotely distributed on multiple electrical busses,operating parameters 302, and/or constraint data 304 may be accessed, atleast in part, via a network. As indicated above, operating parameters302 can include various data associated with an energy storage system,including data related to open circuit voltage, temperature, current(charge or discharge), and/or contactor life.

Constraint data 304 can include power demand data. A power demand can bea part of or determined based on a request for beneficial services suchas peak shaving, frequency response, ramp rate control, purchasing andselling of energy, load following, energy arbitrage, and/or other gridservices. The power demand can specify a requested amount of powerand/or a requested duration. The power demand can specify certainperformance parameters that are mandatory or requested (e.g., suppliedpower should be within a certain frequency range). Constraint data 304can further include data that describes various constraints of an energystorage system. For example, system constraint data 304 can include datathat describes one or more constraints relating to charge or dischargecurrent, charge or discharge power, temperature and/or various otherconstraints associated with the energy storage system.

Further, in some implementations, operating parameters 302 and/orconstraint data 304 can be determined at least in part from one or morefeedback signals provided by one or more energy storage units toperformance model 218 and/or optimizer 216. For example, the feedbacksignals can be provided by energy storage units 102 to performance model218 via sensors 223-225 or other suitable technique. The feedbacksignals can include state of unit data that describes the status ofvarious operating parameters or other present conditions associated withenergy storage units 102. As an example, energy storage units 102 canprovide state of unit data to performance model 218, which can includedata that describes a present power output setpoint of each of the oneor more energy storage units 102, a present effective power output byeach of the one or more energy storage units 102, a present state ofhealth of each of the one or more energy storage units 102, a presentstate of charge of each of the one or more energy storage units 102,internal temperatures, external temperatures, and/or expected change intemperatures at each of the one or more energy storage units 102, apresent and/or expected efficiency for each of the one or more energystorage units 102, inverter information, and/or other data.

Performance model 218 can further receive or obtain data indicative of apresent dispatch state 303 of the energy storage system and/or dataindicative of one or more candidate dispatch states of the energystorage system. The present dispatch state 303 can specify one or moreenergy storage units that are coupled to the system, and that aredecoupled from the system. The one or more candidate dispatch states canspecify various combinations of energy storage units to potentially becoupled to the system, and decoupled from the system. In this manner,upon receiving the various operating parameters 302 and constraint data304, performance model 218 can determine degradation values for thepresent dispatch state 303 and the one or more candidate dispatch statesover one or more time periods. The degradation values can then beprovided to optimizer 216.

In one example implementation, optimizer 216, upon receiving thedegradation values, can be configured to perform a comparison of atleast two of the degradation values during one or more time periods.Optimizer 216 can then be configured to select one or more dispatchstates as selected dispatch states based at least in part on thecomparison. As indicated above, optimizer 216 can be further configuredto select the one or more selected dispatch states based at least inpart on the constraint data. Optimizer 216 can then provide one or moresignals indicative of the selected dispatch state to one or more energystorage units. A dispatch operation of the energy storage system canthen be controlled based at least in part on the signal(s) In exampleembodiments, the signal(s) can further be provided back to performancemodel 218, such that one or more subsequent degradation values can bedetermined.

The optimizer can implement other suitable optimization techniques canbe used without deviating from the scope of the present disclosure. Forinstance, in one embodiment, the optimizer can iteratively determinevarious dispatch states as selected states until an optimum or nearoptimum dispatch state for a present condition is satisfied.

FIG. 4 depicts a flow diagram of an example method (400) of controllinga dispatch operation of an energy storage system according to exampleembodiments of the present disclosure. The method (400) can beimplemented by one or more computing devices, such as one or more of thecomputing devices in FIG. 3. In addition, FIG. 4 depicts steps performedin a particular order for purposes of illustration and discussion, thoseof ordinary skill in the art, using the disclosures provided herein,will understand that various steps of any of the methods discussedherein can be adapted, modified, rearranged, omitted, or expanded invarious ways without deviating from the scope of the present disclosure.

At (402), the method (400) can include receiving or accessing dataindicative of a power demand or commitment. The power demand can specifya requested amount of power and/or a requested duration. The powerdemand can be determined to provide a requested grid service, such aspeak shaving, frequency response, ramp rate control, purchasing andselling of energy, load following, energy arbitrage, and/or other gridservices.

At (404), the method (400) can include receiving data indicative of apresent dispatch state associated with an energy storage system. Inparticular, the present dispatch state can specify the energy storageunits that are presently coupled to the system and/or the energy storageunits that are presently decoupled from the system.

At (406), the method (400) can include identifying one or more candidatedispatch states associated with the energy storage system. A candidatedispatch state can specify one or more energy storage units to becoupled to an energy storage system. In particular implementations, thecandidate dispatch state can further specify one or more energy storageunits to be decoupled from the energy storage system. Each candidatedispatch state can be different from the present dispatch state.

In example embodiments, identifying one or more candidate dispatchstates can include identifying every possible candidate dispatch state.In this manner, each possible candidate dispatch state can be identifiedduring one or more time periods. In alternative embodiments, identifyingone or more candidate dispatch states can include incrementallyidentifying one or more candidate dispatch states during one or moretime periods. Such embodiments are described in more detail below withreference to FIG. 5.

At (408) of FIG. 4, the method (400) can include selecting a candidatedispatch state as a selected dispatch state based at least in part on aperformance model. The performance model can be configured to model theperformance of the energy storage system as a function of one or moreoperating parameters while the energy storage system is operating inaccordance with a candidate dispatch state. For instance, theperformance model can describe expected behavior of the dispatchedenergy storage units under certain described circumstances and in viewof various operating parameters, such as temperature, open circuitvoltage, contactor life, charge or discharge current, and/or variousother suitable operating parameters associated with the dispatchedenergy storage units.

As described above, in example embodiments, a candidate dispatch statecan be selected further based on one or more constraints. In particular,the one or more constraints can include data relating to power demand,battery power, battery current, battery temperature, etc. Theconstraints can vary over time. For instance, a power demand from a gridor other source may change during different times of the day or year. Inaddition, various performance characteristics of the energy storageunits in the energy storage system may change over time. For instance,unit efficiency may decrease throughout the lifetime of an energystorage unit. In this manner, a candidate dispatch state may be selectedas a selected dispatch state only if operating the energy storage systemin accordance with the candidate dispatch state would cause the energystorage system to operate within the bounds of the one or moreconstraints. For instance, a candidate dispatch state may only beselected if the energy storage system would be able to meet the powerdemand when operating in accordance with the candidate dispatch state.

In example embodiments, the constraints can further include data relatedto the states of charge of the energy storage units in the energystorage system. Distributed energy storage units can develop state ofcharge imbalances due at least in part to poor dispatch of the energystorage units to meet the power demand. In such embodiments, thecandidate dispatch state can be selected based at least in part on thestate of charge data. In particular, the constraint can specify adesired state difference value. The desired state difference value canbe indicative of a maximum desired difference between the states ofcharge of the dispatched energy storage units. For instance, the desiredstate difference value can correspond to an average state of charge ofeach energy storage unit in the system. In this manner, one or moreenergy storage units can be coupled to or decoupled from the systembased at least in part on the states of charge of the one or more energystorage units and the desired state difference value.

The candidate dispatch state can be selected by performing anoptimization routine associated with the performance model. Forinstance, the optimization routine can include selecting the candidatedispatch state having the smallest associated degradation value.

In example embodiments, the optimization routine can include identifyinga candidate dispatch state during one or more time periods byincrementally adjusting a number of energy storage units to be coupledto the system. A degradation value may be determined for each identifiedcandidate dispatch state (e.g. for each incremental adjustment) based onthe performance model. The optimization routine can further includecomparing, during each time period, the degradation value associatedwith the candidate dispatch state identified in the present time periodto a candidate dispatch state identified in a previous time period. Inone embodiment, the optimization routine can further include selectingthe present candidate dispatch state as a selected dispatch state whenthe degradation value associated with the candidate dispatch stateidentified in the present time period is less than the degradation valueassociated with the candidate dispatch state identified in the previoustime period.

For instance, FIG. 5 depicts a flow diagram of an example method (500)of an optimization routine for selecting a candidate dispatch state as aselected dispatch over one or more incremental time periods. At (502),method (500) can include identifying a candidate dispatch state duringan initial time period. The candidate dispatch state can specify anumber of energy storage units to be coupled to the system. Forinstance, the candidate dispatch state can be identified byincrementally adjusting the number of energy storage units to be coupledto the system relative to the number of energy storage units specifiedby the present dispatch state (e.g. the number of energy storage unitspresently coupled to the system).

In example embodiments, the incremental adjustment of energy storageunits can be a random incremental adjustment, such that the energystorage units to be coupled to or decoupled from the system are chosenin an arbitrary, random manner. In alternative embodiments, theincremental adjustments can be performed based at least in part on oneor more operating conditions associated with the energy storage system.For instance, an order of adjustment can be determined based at least inpart on the type of energy storage units in the energy storage system,one or more operating parameters associated with the energy storageunits, constraint data associated with the energy storage system, and/orvarious other suitable factors. In a particular implementation, an orderof adjustment can be identified at least in part from a lookup tablestored in a memory associated with the energy storage system. Forinstance, the lookup table can provide one or more orders in which tocouple or decouple energy storage units to the system in view of thevarious operating conditions associated with the energy storage system.In example embodiments, the lookup table can take into account one ormore energy storage units that have been previously coupled to thesystem. For instance, an order of adjustment can be determined such thatan energy storage unit is not coupled to the system if the amount oftime since the energy storage unit was most recently decoupled from thesystem is less than a threshold.

At (504), the method (500) can include inputting one or more operatingparameters into a performance model to determine a degradation valueassociated with the candidate dispatch state. As indicated above, theoperating parameters can include data related to open circuit voltage,temperature, current, contactor life, etc. associated with the energystorage units specified in the candidate dispatch state. Such data canbe used to determine an expected degradation value associated with thecandidate dispatch state.

At (506), the method (500) can include comparing the determineddegradation value with the degradation value of a previous dispatchstate. For instance, during the initial time period, the degradationvalue can be compared to the present degradation value of (404). Duringsubsequent time periods, the degradation value can be compared to thedegradation value associated with the most recently selected dispatchstate.

When the degradation value is less than the degradation value of theprevious dispatch state, the method (500) can include selecting thecandidate dispatch state as a selected dispatch state (508). At (510),the method (500) can include controlling the energy storage system inaccordance with the selected dispatch state. In this manner, one or moreswitches coupled to one or more energy storage units can be selectivelycontrolled to couple the one or more energy storage units to the systemin accordance with the selected dispatch state, such that the number ofenergy storage units coupled to the system corresponds to the number ofenergy storage units specified in the selected dispatch state.

At (512), the method (500) can include identifying a subsequentcandidate dispatch state during a subsequent incremental time period. Inparticular, upon the expiration of a previous time period (e.g. theinitial time period of (502)), a subsequent candidate dispatch state canbe identified by incrementally adjusting the number of energy storageunits to be coupled to the system relative to the most recently selecteddispatch state. The method (500) can then return to (504).

Referring back to (506), if the degradation value is not less than thedegradation value associated with the previously selected dispatchstate, the method (500) can bypass (508) and (510), and can proceeddirectly to (512). In this manner, if the degradation value is not lessthan the previously selected degradation value, the candidate dispatchstate is not selected.

Referring back to FIG. 4 at (410), method (400) can include controllingthe operation of the energy storage system based at least in part on theselected dispatch state. For instance, the energy storage system can becontrolled to operate in accordance with the selected dispatch states.For instance, the energy storage system can be controlled by selectivelycontrolling one or more switches (e.g. contactors) coupled to one ormore energy storage units to couple the one or more energy storage unitsto the system in accordance with the selected dispatch state, such thatthe number of energy storage units coupled to the system corresponds tothe number of energy storage units specified in the selected dispatchstate.

Although specific features of various embodiments may be shown in somedrawings and not in others, this is for convenience only. In accordancewith the principles of the present disclosure, any feature of a drawingmay be referenced and/or claimed in combination with any feature of anyother drawing.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A method of actively controlling a dispatchoperation of an energy storage system, the method comprising: receiving,by one or more control devices, data indicative of a present dispatchstate associated with an energy storage system, the energy storagesystem comprising a plurality of energy storage units coupled inparallel, the present dispatch state specifying the energy storage unitspresently coupled to the system; identifying, by the one or more controldevices, one or more candidate dispatch states associated with theenergy storage system, each of the one or more candidate dispatch statesbeing different from the present dispatch state; selecting, by the oneor more control devices, at least one of the one or more candidatedispatch states as a selected dispatch state based at least in part on aperformance model, the performance model modeling the performance of theone or more candidate dispatch states as a function of one or moreoperating parameters; and controlling, by the one or more controldevices, operation of the energy storage system based at least in parton the selected dispatch state.
 2. The method of claim 1, wherein theoperating parameters are measured operating parameters.
 3. The method ofclaim 1, wherein selecting, by the one or more control devices, thecandidate dispatch state as a selected dispatch state based at least inpart on a performance model, comprises: determining, by the one or morecontrol devices, a degradation value for each of the one or morecandidate dispatch states based on the performance model; and selecting,by the one or more control devices, the candidate dispatch state as theselected dispatch state based at least in part on the degradation value.4. The method of claim 3, wherein identifying, by the one or morecontrol devices, the selected dispatch state based at least in part onthe degradation value comprises performing an optimization routine basedat least in part on the performance model.
 5. The method of claim 4,wherein the optimization routine comprises: during each of a pluralityof time periods, identifying, by the one or more control devices, acandidate dispatch state by incrementally adjusting a number of energystorage units to be coupled to the system; and for each candidatedispatch state, determining, by the one or more control devices, adegradation value for the candidate dispatch state associated with theincremental adjustment.
 6. The method of claim 5, wherein incrementallyadjusting a number of energy storage units to be coupled to the systemcomprises decreasing or increasing a number of energy storage units tobe coupled to the system.
 7. The method of claim 1, wherein the one ormore operating parameters comprise at least one of an open circuitvoltage, a temperature, a current or a contactor life associated withthe respective energy storage units.
 8. The method of claim 1, whereinthe one or more candidate dispatch states are identified at least inpart from a lookup table associated with the energy storage system. 9.The method of claim 1, wherein the performance model takes into accountone or more constraints.
 10. The method of claim 10, wherein the one ormore constraints comprise at least one of the power commitment, a power,a current, a voltage characteristic, or a temperature associated withthe energy storage system.
 11. The method of claim 1, whereincontrolling, by the one or more control devices, operation of the energystorage system based at least in part on the selected dispatch statecomprises coupling one or more energy storage devices to the energystorage system in accordance with the selected dispatch state.
 12. Anenergy storage system comprising: a plurality of energy storage unitscoupled in parallel; and a system controller communicatively coupled toa plurality of contactors used to selectively couple the plurality ofenergy storage units to the energy storage system, the system controllercomprising at least one processor and a non-transitory computer-readablemedium storing instructions that, when executed by the at least oneprocessor, cause the system controller to perform operations, theoperations comprising: receiving data indicative of a present dispatchstate associated with the energy storage system, the present dispatchstate specifying the energy storage units presently coupled to thesystem; identifying one or more candidate dispatch states associatedwith the energy storage system, each of the one or more candidatedispatch state being different from the present dispatch state;selecting at least one of the one or more candidate dispatch states as aselected dispatch state based at least in part on a performance model,the performance model modeling the performance of the one or morecandidate dispatch states as a function of one or more measuredoperating parameters; and controlling operation of the energy storagesystem based at least in part on the selected dispatch state.
 13. Theenergy storage system of claim 12, wherein selecting the candidatedispatch state as a selected dispatch state based at least in part on aperformance model comprises: determining a degradation value for each ofthe one or more candidate dispatch states; and selecting the candidatedispatch state as the selected dispatch state based at least in part onthe degradation value.
 14. The energy storage system of claim 12,wherein identifying the selected dispatch state based at least in parton the degradation value comprises performing an optimization routinebased at least in part on the performance model.
 15. The energy storagesystem of claim 14, wherein the optimization routine comprises: duringeach of a plurality of time periods, identifying a candidate dispatchstate by incrementally adjusting a number of energy storage units to becoupled to the system; and for each candidate dispatch state,determining a degradation value for the candidate dispatch stateassociated with the incremental adjustment.
 16. The energy storagesystem of claim 15, wherein the optimization routine further comprises:during each time period of the plurality of time periods, comparing thedegradation value associated with the candidate dispatch stateidentified in the present time period with the degradation valueassociated with the candidate dispatch state identified in the previoustime period; and selecting the present candidate dispatch state as aselected dispatch state when the degradation value associated with thecandidate dispatch state identified in the present time period is lessthan the degradation value associated with the candidate dispatch stateidentified in the previous time period.
 17. A system controller forcontrolling one or more energy storage units in an energy storagesystem, the system controller comprising at least one processor and anon-transitory computer-readable medium storing instructions that, whenexecuted by the at least one processor, cause the system controller toperform operations, the operations comprising: receiving data indicativeof a present dispatch state associated with an energy storage system,the energy storage system comprising a plurality of energy storage unitscoupled in parallel, the present dispatch state specifying the energystorage units presently coupled to the system; identifying one or morecandidate dispatch states associated with the energy storage system,each of the one or more candidate dispatch state being different fromthe present dispatch state; selecting at least one of the one or morecandidate dispatch states as a selected dispatch state based at least inpart on a performance model, the performance model modeling theperformance of the one or more candidate dispatch states as a functionof one or more measured operating parameters; and controlling operationof the energy storage system based at least in part on the selecteddispatch state.
 18. The system controller of claim 17, wherein selectingthe candidate dispatch state as a selected dispatch state based at leastin part on a performance model comprises: determining a degradationvalue for each of the one or more candidate dispatch states; andselecting the candidate dispatch state as the selected dispatch statebased at least in part on the degradation value.
 19. The systemcontroller of claim 17, wherein identifying the selected dispatch statebased at least in part on the degradation value comprises performing anoptimization routine based at least in part on the performance model,and wherein the optimization routine comprises: during each of aplurality of time periods, identifying a candidate dispatch state byincrementally adjusting a number of energy storage units to be coupledto the system; and for each candidate dispatch state, determining adegradation value for the candidate dispatch state associated with theincremental adjustment.
 20. The system controller of claim 19, whereinthe optimization routine further comprises: during each time period ofthe plurality of time periods, comparing the degradation valueassociated with the candidate dispatch state identified in the presenttime period with the degradation value associated with the candidatedispatch state identified in the previous time period; and selecting thepresent candidate dispatch state as a selected dispatch state when thedegradation value associated with the candidate dispatch stateidentified in the present time period is less than the degradation valueassociated with the candidate dispatch state identified in the previoustime period.